This cross-section of a tunnel in the planned disposal facility under Yucca Mountain in the Nevada desert, shows three types of waste container: fuel assemblies for pressurised water reactors and boiling water reactors (in the foreground and background), and high-level waste packages (in the middle). Note the titanium drip shields designed to protect the containers against water dripping from the tunnel roof. Although Yucca Mountain is subject to a desert climate, layers of tuff (compacted ash) are not as impermeable as clay. This was one of the reasons for which the project was abandoned.